Allow byte streams with unknown type to be compatiable with binary (#12959)

# Description
Currently, this pipeline doesn't work `open --raw file | take 100`,
since the type of the byte stream is `Unknown`, but `take` expects
`Binary` streams. This PR changes commands that expect
`ByteStreamType::Binary` to also work with `ByteStreamType::Unknown`.
This was done by adding two new methods to `ByteStreamType`:
`is_binary_coercible` and `is_string_coercible`. These return true if
the type is `Unknown` or matches the type in the method name.

crates/nu-command/src/conversions/into/string.rs

@@ -160,7 +160,7 @@ fn string_helper(
         // Just set the type - that should be good enough. There is no guarantee that the data
         // within a string stream is actually valid UTF-8. But refuse to do it if it was already set
         // to binary
-        if stream.type_() != ByteStreamType::Binary {
+        if stream.type_().is_string_coercible() {
             Ok(PipelineData::ByteStream(
                 stream.with_type(ByteStreamType::String),
                 metadata,